Need help with Mendel90 Pronterface/Slice3r settings Our problem is the machine prints in mid

3D Printing
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Need help with Mendel90 Pronterface/Slice3r settings
Our problem is the machine prints in mid air (up near Z home limit switch).
Machine has Melzi controller. We’re using Slice3r and Pronterface.
Our Z_HOME_POS in Arduino is 187.3. When we manually move Z axis the machine knows where it is (when we home the Z axis and check position in Pronterface it is correct). We can use Pronterface to freely manually move Z axis anywhere from bed to limit switch. However, when we print a part and the G code instructs the Z axis to go to 0.05mm, it actually just moves approx. 10mm below Z limit switch and starts printing.

Arduino Settings
#define INVERT_X_DIR false // for Mendel set to false, for Orca set to true
#define INVERT_Y_DIR false // for Mendel set to true, for Orca set to false
#define INVERT_Z_DIR true // for Mendel set to false, for Orca set to true
#define INVERT_E0_DIR true // for direct drive extruder v9 set to true, for geared extruder set to false
#define INVERT_E1_DIR false // for direct drive extruder v9 set to true, for geared extruder set to false
#define INVERT_E2_DIR false // for direct drive extruder v9 set to true, for geared extruder set to false

// ENDSTOP SETTINGS:
// Sets direction of endstops when homing; 1=MAX, -1=MIN
#define X_HOME_DIR -1
#define Y_HOME_DIR -1
#define Z_HOME_DIR 1

#define X_HOME_POS (X_MIN_POS - 1)
#define Y_HOME_POS (Y_MIN_POS - 1)
#define Z_HOME_POS (187.3)
////////////////// I tried changing Invert_Z_Dir and Invert_Y_Dir settings above but that starting driving machine upwards into Z limit switch so I abandoned that ////////////////////////////////////

Pronterface settings picture below

Slic3r settings picture below
(file from an old post on Slicer Settings for the Mendel90 )

Slice 3r Start G code
M83 ; relative werte nutzen
G28 ; home all axes
G92 E0 ; reset extruder
G1 Y-98 X-98 F4000
G1 Z0.05 F30000
M190 S60
M109 S200

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I resolved this (after much searching through multiple forums). It turns out the Marlin code was not suitable for my motors and steps were being skipped. The original code was:
#define DEFAULT_MAX_FEEDRATE {400, 400, 4, 30} // (mm/sec)
and I changed the settings to 200,200,2,30 (I reduced X and Y values in addition to Z since I was observing some slight shuddering on X,Y movement).
I was also having Z homing extreme shuddering issues and corrected this on Marlin code
#define HOMING_FEEDRATE {3560, 3560, 4*60, 0} // set the homing speeds (mm/min)
where I changed the 4 to 2.
I will revisit these numbers later to optimize them but for now the axis movement is very good and I can move on to the next issue (I am struggling to find the correct combo of Slice3r and Pronterface settings to print in the center of the bed - the machine is printing at the edges of the bed). I’ve changed the Slice3r Print Center settings (from 0,0 to 100,100) but that shifted my print location to opposite edge.